1. Field of the Invention
The present invention related to a magnetic head used in thermal-assisted magnetic recording and a magnetic recording system including the magnetic head.
2. Background Art
The information recording density of magnetic recording systems continues to increase, and the size of magnetic recording marks of 1 bit continues to be smaller. In the magnetic recording systems, the miniaturization of the recording bit size is mainly attained by the miniaturization of the size of the recording magnetic head and the miniaturization of the magnetic particles of the magnetic recording medium. However, it is feared that the magnetization information recorded in the magnetic recording medium disappears in a short time at room temperature due to thermal fluctuation when the recording density is over about 1 Tbit/inch2. To prevent this, the coercive force of the magnetic recording medium needs to be increased. However, there is a limit to the intensity of the magnetic field that can be generated from the magnetic recording head. Therefore, the recording bit cannot be formed in the medium if the coercive force is increased too much. To solve this, a thermal-assisted magnetic recording system that allows recording to the high coercive force medium by heating the medium at the moment of recording to reduce the coercive force is drawing attention in recent years. So far, a method for realizing the high recording density by emitting a minute light spot on the medium at high power density to locally heat only the recording area is proposed as the thermal-assisted magnetic recording system.
A lens is typically used to generate the minute light spot, and in recent years, the distance between the magnetic head and the magnetic recording medium is 10 nm or less. If the weight increases by mounting an optical element, such as the lens, on the magnetic head, the weight causes a problem that the magnetic recording head touches the magnetic recording medium or that the head cannot fly. A plurality of magnetic recording media (disks) are laminated in the magnetic recording system, and the intervals between the magnetic recording media are usually 1 mm or less. Therefore, the height of all components installed around the magnetic head need to be within 1 mm. Therefore, it is not preferable to mount an optical element, such as a large lens used in an optical disk recording/reproducing apparatus, on the magnetic head.
An example of a method of generating a minute light spot on the magnetic recording medium without using a lens, etc. includes a method of forming a waveguide including a core and a clad in the magnetic head. The method can be realized by forming a core having a width and a thickness of submicron order by a high-refractive-index material. In Japanese Journal of Applied Physics, Vol. 45, No. 2B, 2006, pp. 1314-1320, an optical waveguide called Planer Solid Immersion Mirror is used in which the width of the core is circularly narrowed down toward the propagation direction of light. However, a grating is used to couple the incident light to the optical waveguide, and a light propagation loss is feared due to an optical axis misalignment of the incident light. In Optics Letters, Vol. 28, No. 15, 2003, pp. 1302-1304, an optical waveguide, in which a core in the size of several dozen nm is thickened in a taper shape toward the propagation direction of light, is used to couple light with a relatively large spot size to the optical waveguide. The spot size is reduced to submicron order, while the light is propagated in the optical waveguide. In JP2007-257753A, the taper-shaped core is used to form the optical waveguide in the magnetic head.